Two-stage ORVR control valve

ABSTRACT

A refueling fuel level responsive control valve with a two-stage closing operation providing an initial soft shutoff cue to the filler nozzle operator, and a subsequent final shutoff after a limited amount of &#34;roundoff&#34; filling to a maximum fuel level. The control valve includes two float-operated valve elements which close serially in response to initial shutoff and final shutoff refueling fuel levels. The initial shutoff partially closes the control valve to create a temporary shutoff-inducing increase in fuel tank pressure. Final shutoff occurs after allowing a few round-off &#34;clicks&#34; of the filler nozzle to fully close venting through the control valve.

This application is a continuation application of U.S. Ser. No.08/769,166 filed Dec. 18, 1996 (now U.S. Pat. No. 5,860,458 issued Jan.19, 1999), which is a continuation of U.S. Ser. No. 08/295,196 filedAug. 24, 1994 (now U.S. Pat. No. 5,590,697 issued Jan. 7, 1997).

FIELD OF THE INVENTION

The present invention relates generally to control valves for "onboard"type fuel vapor recovery systems for vehicle fuel tanks, wherein fuelvapor generated during the refueling process is vented to onboard vaporrecovery apparatus such as a carbon canister.

BACKGROUND OF THE INVENTION

Systems for controlling the flow of fuel vapor from a vehicle fuel tankto a recovery apparatus such as a carbon canister are generally known. Acommon approach is to place a control valve in series between the fueltank and the vapor trap to selectively open and close the vapor ventingpathway in response to changes in vehicle refueling activity.

Some known vapor control valves open or close in response to pressureconditions at the filler pipe inlet, for example when a filler pipe capis removed or replaced to indicate the start or finish of refuelingoperations.

Other pressure-operated control valves respond to vapor pressure in thefuel tank itself to open, close, or adjust the rate at which fuel vaporis vented.

Another known type of valve responds to the level of liquid fuel in thetank, staying open to vent vapor as long as the fuel level is below apredetermined level. These are sometimes referred to as "fill control"or "shutoff" valves, since their closing creates a sudden pressureincrease in the tank which prevents further refueling.

Prior vapor recovery systems often use pressure-operated control valves,sometimes supplemented with rollover and/or fill control valves tosupplement the pressure operated vapor control. Disadvantages of suchpressure-operated systems include their relative complexity and cost;their sensitivity to changing pressure conditions in the fuel system;and, the need for vapor seal and/or signal structure in the filler pipe,for example filler nozzle trap doors and signal pressure lines toprevent the loss of fuel vapor to the atmosphere during refueling and/orto provide signal or actuation pressure to the control valve.

One known technique for eliminating filler nozzle trap door or otherseal structure in the filler pipe is to create a "dynamic" seal in thepipe using only the flow effects of a high velocity stream of fuel fromthe filler nozzle. By properly shaping the filler pipe in the regionwhere the filler nozzle is located during refueling, and pumping thefuel at high velocity, a vacuum or draw-type seal can be created andmaintained around the filler nozzle during refueling. This eliminatesthe need for seal door and similar structure. However, manypressure-operated control valves cannot function without such structurein the filler pipe. The dynamic sealing generates higher refuelingpressure in the tank, tending to cause undesirable fuel expulsion or"spitback" from the filler pipe inlet at the end of the refuelingoperation. The prior art has not adequately addressed the need for anonboard vapor recovery system suitable for high pressure refueling witha dynamic filler pipe seal.

SUMMARY OF THE INVENTION

The present invention is a refueling fuel level responsive control valvecomprising a two-stage shutoff valve with a cushioned, "soft" initialshutoff especially suited for high-pressure refueling operations, forexample with dynamically sealed filler pipes, but useful generally forrefueling-operated shutoff in a vehicle fuel tank. The inventive controlvalve is adapted for venting fuel vapor from the fuel tank to a vaporrecovery apparatus at a first higher rate when the fuel level is belowan initial refueling shutoff level; at a second lower rate when the fuellevel reaches the initial shutoff level, such that a shutoff-inducingpressure increase is temporarily created in the tank for a "soft"shutoff; and for closing when a maximum refueling shutoff level isreached. This is achieved in a particular embodiment with a two-stagevalve closing structure responsive to the level of liquid fuel in thetank, wherein primary and secondary valve elements operated by a floatfirst partially close, and then fully close, the control valve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a vehicle fuel system with anonboard vapor recovery system according to the present invention;

FIG. 2 is a section view of a fuel level responsive control valveemployed in the system of FIG. 1;

FIG. 2A illustrates the valve of FIG. 2 in a fully closed condition;

FIGS. 3 and 3A are section views of an alternate control valve for usein the system of FIG. 1;

FIG. 4 is a section view of a rollover valve for use with the system ofFIG. 1;

FIG. 5 is a section view of a liquid seal check valve for use in thefiller pipe of FIG. 1;

FIG. 5A illustrates the check valve of FIG. 5 in an open condition; and

FIG. 6 illustrates the system of FIG. 1 during a refueling operation.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIG. 1, an onboard vapor recovery system according tothe present invention is shown for a vehicle fuel system comprising atank 10, a filler pipe 12 with an inlet 14 selectively closed by cap 16,and a vapor canister 18 connected to tank 10 by a vent line 17. Thefiller pipe in the inventive system is configured to create a dynamicseal with a filler nozzle during refueling; i.e., fuel pumped at highvelocity from the filler nozzle into the filler pipe creates avacuum-type seal adjacent the filler nozzle outlet to prevent the escapeof fuel vapor out the filler pipe inlet. In the illustrated embodimentthe dynamic seal results in fuel being introduced into the tank at apressure head of approximately eighteen to twenty inches of waterpressure. Prior systems without dynamic sealing often operate atrefueling pressures of around seven to ten inches.

Fuel vapor from tank 10 is vented through line 17 to canister 18, whereit is adsorbed and periodically purged to the engine for combustion.Fuel vapor venting from tank 10 via line 17 to canister 18 is through afuel level responsive control valve 20, mounted in a suitable aperturein the fuel tank to be closed by liquid fuel at or above a predeterminedlevel shown at 11. When the liquid fuel in tank 10 is below thatpredetermined level, valve 20 remains open to vent fuel vapor tocanister 18.

In the illustrated embodiment control valve 20 substantially reduces,but does not abruptly halt, vapor venting from the tank to the vaporcanister when an approximate full fuel level is reached. Instead, valve20 provides a limited amount of additional, low volume vapor ventingbetween a first full level and a slightly higher maximum "round off"level. This results in an initial "soft" shutoff at the first full levelto prevent overly rapid backup of fuel in the filler pipe and possiblespitback onto the person operating the filler nozzle. When the initialshutoff occurs, the resulting rise in tank pressure forces fuel back upthe filler pipe to cover the mouth of the filler nozzle, activating aninternal shutoff mechanism in the filler nozzle in known manner. After ashort time the fuel standing in the filler pipe drains back into thetank. If the nozzle operator continues to fill the tank after being cuedby the initial shutoff, the valve closes at the maximum level to triggera final shutoff and end the refueling activity.

The illustrated system also includes a rollover-type head valve 22, inthe illustrated embodiment of FIG. 1 a separate valve 22 mounted in thefuel tank to vent fuel vapor to canister 18 through line 23. Rolloverhead valve 22 is designed to maintain a sufficient pressure head in thevapor space of the fuel tank after valve 20 has closed for fuel toaccumulate in the filler pipe for nozzle shutoff. For example, headvalve 22 maintains approximately twenty inches of water pressure. Belowthis pressure rollover head valve 22 remains closed; above this pressurerollover head valve 22 opens to rapidly vent fuel vapor to canister 18.In the illustrated embodiment of FIG. 1, rollover head valve 22 includesa small bleed orifice or vent, for example on the order of 0.020 inchesdiameter, to provide a low volume, continuous vent from the fuel tank tothe canister. As described below, the bleed in valve 22 providessufficient head valve function on its own if pressure reduction afterfill occurs within a reasonable time.

Still referring to FIG. 1, the illustrated system also includes a oneway, low back pressure, liquid seal check valve 24 in the lower end ofthe filler pipe at or below the full fuel level. High velocity fuelintroduced from the upper end of the filler pipe during refueling forcescheck valve 24 open to fill the fuel tank. When control valve 20 closesto seal the tank and refueling ceases, check valve 24 positively closesagainst the pressurized fuel in the tank to prevent it from beingexpelled out the filler pipe.

The one way nature of check valve 24 prevents its being forced open forreverse fluid flow from the tank to the filler pipe.

Vacuum relief for the fuel tank is provided by suitable vacuum reliefstructure 15 in cap 16 of a known type, acting in series with checkvalve 24. For example, if negative pressure conditions occur in thevapor space in tank 10, the pressure imbalance across check valve 24will cause it to open, relieving the tank with pressure stored in fillerpipe 12. If this residual pressure is not enough to relieve the tankvacuum, the vacuum relief valve structure 15 in cap 16 will additionallyopen to provide atmospheric relief pressure through pipe 12 and checkvalve 24 to the tank. This arrangement complements the inherent vacuumrelief structure in either of valves 20 or 22. The bleed in valve 22 mayprovide some vacuum relief prior to relief through cap 16; and vacuumrelief can sometimes occur across the float structure in valve 20, whichcan be forced downwardly against liquid fuel if the vacuum pressuredifferential across it is high enough.

FIG. 1 illustrates the vehicle fuel system immediately after the tankhas been filled to the maximum level and refueling has ceased. In thiscondition control valve 20 is closed, rollover head valve 22 is closed(assuming a pressure head in tank 10 at or below the pressure relieflevel of the rollover head valve), and check valve 24 is closed. Acolumn of liquid fuel (not shown) may remain standing in the filler pipeabove the check valve. Except for the low volume bleed vent in rolloverhead valve 22, the entire system is closed.

The low volume bleed vent in rollover head valve 22 dissipates theclosed system pressure to the canister, maintaining the pressure headfor a short time (for example, less than one minute) after the checkvalve 24 and shutoff valve 20 have closed. Temporarily maintaining theclosed system pressure head in this manner discourages attempts atoverfilling for a reasonable period, and then allows tank pressure todecay so that standing fuel in the filler pipe can drain into the tankand overall system pressure is reduced.

Should tank pressure increase in this closed system condition beyond thecapacity of the bleed vent, for example if the vehicle is left parkedwith the tank at maximum fuel level and at high temperature, therollover head valve 22 opens for rapid venting until the excess pressureis relieved. In this extreme case, the tank pressure will notsignificantly exceed the twenty-inch head maintained by the head valve,although some hysteresis in pressure reduction may initially occurdepending on the exact rollover structure used.

It should be noted that the check valve 24 will remain closed by thespring and the high fuel level if the cap is removed, preventing fuelexpulsion. If the vehicle is driven in this closed-system condition,fuel sloshing will intermittently open shutoff valve 20, which willrapidly reduce tank pressure.

A vent line 21 from valve 20 to the atmosphere provides emergencypressure relief in a manner described below in reference to FIG. 2.

The control valve 20 of the present invention is open both duringrefueling and normal vehicle operation, so long as the fuel level in thetank is below the maximum (i.e., reopening) level, which those skilledin the art will recognize as varying slightly as the result of differenttank pressures and the effects of hysteresis. Vapor is accordinglyvented to the canister 18 on a relatively continuous basis. To preventsaturation of the canister with fuel vapor, an electronic purge solenoid19 is connected downstream from the canister to periodically allowvacuum from the vehicle intake manifold to "purge" vapor from thecanister to the engine.

It can be seen from the foregoing that the fuel level responsive controlvalve 20, head valve 22 and check valve 24 provide complementary vaporrecovery, shutoff and spitback-prevention in a manner uniquelycoordinated for high pressure refueling with a dynamically-sealed fillerpipe. Fuel level responsive valve 20 is unaffected by pressure extremesand vents freely until the tank is filled, at which point its cushionedshutoff provides a first level of spitback protection against the highpressure refueling. Head valve 22 maintains the high pressure headneeded in the tank to provide a shutoff-inducing back pressure aftervalve 20 has closed, at least long enough to discourage overfillingattempts, and then reduces overall pressure with a controlled bleed.Check valve 24 provides an immediate, reliable check against spitbackfrom the tank pressure accumulated for the shutoff function. Check valve24 also maintains a back pressure low enough to avoid premature shutoffof the filler nozzle.

Referring now to FIG. 2, a first embodiment of a shutoff type controlvalve suitable for the system of FIG. 1 is illustrated. Valve 20comprises an essentially hollow valve body mounted in a suitableaperture in the fuel tank. Lower half 42 of the valve is located in theinterior of the fuel tank, and communicates with an upper half 44outside the fuel tank. The valve is fastened to the fuel tank in liquid-and vaportight manner by connector flange 46, for example by hot platewelding, ultrasonic welding, grommet-type seal or other knowntechniques.

Lower half 42 of valve 20 defines a float chamber 48 open at its lowerend to receive liquid fuel as the fuel level in the tank rises to thefull level. Radial vent ports 43 and holes 47 in the bottom end of lowerhalf 42 provide vapor and liquid communication between tank 10 and floatchamber 48. At its upper end float chamber 48 includes a primary ventport 50 opening into the upper half 44 of the valve and communicatingwith an outlet 52 connected by conduit or hose 17 (FIG. 1) to vaporcanister 18.

Valve 20 can be provided with baffle structure (not shown) associatedwith vent ports 43 in chamber 48, to prevent liquid fuel from splashingthrough vent ports 43 to port 50.

Chamber 48 also includes a pressure relief port 54 at its upper end,opened and closed by spring-biased pressure relief valve 56 toselectively vent chamber 48 to a pressure relief outlet 58 connected tothe atmosphere (by line 21 in FIG. 1).

A fuel level responsive float 49 is contained in chamber 48 for up anddown movement on guide pins 49a as the float chamber fills with liquidfuel through holes 47 and vents 43. The density of float 49 is balancedrelative to that of the fuel, for example with a spring 49b, such thatit closes when immersed in liquid fuel in both upright and rolloversituations. Float 49 may have a density less than, equal to, or greaterthan that of the fuel, balanced by spring 49b as desired for fillcontrol and rollover function.

Referring to FIGS. 2 and 2A, the upper end of float 49 is connected byspindle 49c to a first valve cage 60 defining a cylindrical cupcontaining a primary shutoff valve element 62. Primary valve element 62is axially trapped in cage 60 by interference between its shoulder 64with lip 61 on cage 60. Valve element 62 includes a number of ventapertures 66 which allow vapor communication between float chamber 48and the interior of valve cage 60. Valve element 62 also includes acentral vent passageway 68 aligned with vent port 50. Primary valveelement 62 is normally forced against lip 61 at the upper end of cage 60by a spring 70. Valve element 62 supports a sealing member 72 at itsupper end, for example a resilient rubber-like disc retained by anangled collar 69.

A second valve cage 74 is formed inside valve cage 60, containing asecondary valve disk 76. Valve cage 74 comprises a plurality ofactuation fingers 78 of varying height around the periphery of valvedisk 76. Valve disk 76 is free to move axially within cage 74 betweenthe upper ends of fingers 78 and a centering bead. Second valve cage 74and secondary valve 76 can comprise, for example, peeling action valvestructure of the type shown and described in U.S. Pat. No. 4,753,262 toR. Bergsma, co-owned by the assignee of this application.

In operation, float 49 and the primary and secondary valve elements62,76 remain in a lower position in float chamber 48 away from primaryvent port 50 whenever the fuel level is below a predetermined level.

When the fuel reaches a predetermined near-full level, float 49 rises inchamber 48, forcing seal 72 on primary valve element 62 against theprimary vent port 50. This closes primary vent port 50, but leaves openthe lower volume venting from chamber 48 through valve cage 60 viaapertures 66 and passageway 68 in valve 62. The result is a significantreduction in the rate of vapor venting, causing a rapid but controlledrise in the tank head pressure. This in turn forces fuel back up thefiller pipe at a controlled rate, actuating the filler nozzle mechanismfor an initial "soft" shutoff without spitback onto the operator.

The initial shutoff is a cue to the operator that the tank is close tofull. At this point primary valve 62 is in the position shown in FIG. 2,above valve disk 76 resting in cage 74, held in place by the force ofspring 70.

After the initial soft shutoff and the shutoff-inducing rise in tankpressure, vapor pressure in the tank is dissipated fairly quickly, forexample in a few seconds, through the secondary vent path defined byapertures 66 and passageway 68. This allows the fuel backed up in thefiller pipe to drain into the tank. As a result, a small amount ofadditional fuel can be added to round off the tank by "clicking" thefiller nozzle operating handle.

If the nozzle operator should choose to add fuel after the initialshutoff, float 49, cage 60 and cage 74 are forced upwardly by the risingfuel against spring 70 until valve disk 76 contacts and closes offcentral passageway 68 in valve 62 as shown in FIG. 2a. This completelycloses venting from the fuel tank through valve 20 to canister 18, andresults in a final shutoff cue to the operator of the filler nozzle.Should the operator ignore these shutoff indicatinos and unwiselypersist in trying to add fuel beyond the initial shutoff and the fewround-off "clicks" allowed before final shutoff cue, and somehowoverride or circumvent the filler nozzle shutoff mechanism, the fuelwill simply back out the filler pipe inlet.

The two-stage soft shutoff with its cushioned initial shutoff andcontrolled round-off allowance can be adjusted as desired through therelative sizing of the primary and secondary vent ports or passages,spring forces, the relative height of the first and second valvescontrolling the amount of round-off, and in other ways which will beapparent to those skilled in the art. In the illustrated embodiment theprimary and secondary valve elements 62,76 are calibrated to permitthree or four clicks of round-off before completely closing the valve.

Valve 20 remains fully closed until the level of liquid fuel in the tankdrops, with valve disk 76 first being peeled off passageway 68 byfingers 78 as float 49 drops, followed by valve 62 being pulled fromvent port 50 by valve cage 60 as the float drops further.

Pressure relief valve 56, located above the maximum fuel level, isforced open against spring 57 when vapor pressure in the tank exceeds apredetermined safe level, for example sixty inches water pressure. Valve56 would then open to reduce tank pressure to a safe level. Theinfrequency and nature of emergency pressure venting warrants ventingvalve 56 to the atmosphere for immediate pressure reduction.

FIGS. 3 and 3A illustrate an alternate two-stage soft shutoff valve 120suitable for the system of FIG. 1. Its operation is similar to that ofthe valve in FIG. 2, but the primary and secondary valves are radiallyoffset, rather than coaxially arranged.

In FIG. 3 a primary vent port 150 and a secondary vent passage 168 areradially spaced from one another at the upper end of float chamber 148.Vents 150, 168 vent vapor from the tank to the upper half 144 of valve120, where it passes to a vapor trap through outlet 152. Spring balancedfloat 149 supports a primary valve 162 for closing primary vent 150, anda secondary valve 176 for closing passageway 168. Primary valve 162 isnormally positioned higher than valve 176 by bias spring 170.

Secondary valve 176 may, for example, be the peel-away type illustratedin U.S. Pat. No. 5,313,977 to Bergsma et al, co-owned by the assignee ofthe present application, including a valve element 178 and peel-awaystructure 180.

Float 149 and valves 162,176 remain below the vent ports 150,168 as longas liquid fuel is below the full or near-full level. When fuel in floatchamber 148 reaches the predetermined "soft" shutoff level throughradial and/or axial ports 143, 147 in lower half 142, float 149 isforced upwardly to initially close primary vent port 150 with valve 162.This initiates the initial soft shutoff described above. If the operatoradds additional fuel by clicking the filler nozzle, float 149 is liftedfurther against spring 170 until second valve 176 contacts and closesoff the secondary passageway 168 as shown in FIG. 3A. This finalizes theshutoff of control valve 120 in the manner described above in FIG. 2.

Valve 120 opens in a manner similar to valve 20 described in FIG. 2;i.e., valve 176 is first peeled off passageway 168 by the descendingfloat, followed by valve 162 being pulled away from primary vent outlet150 as the fuel level drops further. It will be apparent to thoseskilled in the art that, despite the different structure, valve 120 inFIG. 3 achieves a two-stage soft shutoff similar to that of valve 20 inFIG. 2. It is therefore suitable for use with the system of FIG. 1 inplace of valve 20.

FIG. 4 illustrates one embodiment of a rollover-type head valve 22suitable for use in the system of FIG. 1. Rollover head valve 22comprises an essentially hollow body mounted to the fuel tank 10 througha suitable aperture via a shoulder portion 22b and resilient sealmembers 22c and 22d. Rollover head valve 22 has an upper half 22elocated outside the tank and including an outlet 22f connected to thevapor canister as shown in FIG. 1 by suitable hose or conduitconnection. A lower half 22g of the rollover head valve extends into thefuel tank, and includes a rollover float chamber 22h. At its upper endfloat chamber 22h communicates with outlet 22f by way of a rollover ventoutlet 22i and a head valve vent outlet 22j. Rollover vent outlet 22i isselectively closed by a spring balanced rollover float valve 22k held infloat chamber 22h, and head valve vent outlet 22j is normally closed bya ball-type head valve 22l. Float chamber 22h includes a number ofradial vent ports 22m through which fuel vapor from the tank can enterfloat chamber 22h and pass through vent outlets 22i,22j to rollover headvalve outlet 22f and the vapor canister. Float chamber 22h also includesa hole 22n in its end plate 22o through which liquid fuel enters thefloat chamber to raise float 22k when the liquid level in the tank risesto the level of rollover head valve 22.

Further explanation of the structure and operation of a rollover valvesimilar to 22k and a head valve similar to 22l is found in U.S. Pat.Nos. 5,313,977 to Bergsma et al and 5,253,668 to Mills, respectively,both co-owned by the assignee of this application.

FIG. 4 illustrates rollover head valve 22 in its normally closedcondition for an upright vehicle orientation. The level of liquid fuelin the tank, even at maximum, remains below the level of rollover headvalve 22, leaving rollover float valve 22k in the lowered position awayfrom rollover vent outlet 22i. However, ball head valve 22l iscalibrated to maintain a pressure head in the fuel tank higher than thepressure at which fuel is introduced into the tank during refueling oncethe shutoff control valve 20 has closed. Ball head valve 22l accordinglyremains in the closed position shown in solid lines in FIG. 4 in whichthe head valve vent outlet 22j is blocked by the ball valve element.

Rollover head valve 22 also includes a small bleed vent 22p,illustratively associated with the ball head valve outlet 22j, toprovide a continuous, low volume vent from the fuel tank to the canisterthrough rollover head valve 22 even in the valve closed condition ofFIG. 4. Bleed vent 22p is calibrated to gradually reduce the pressurehead maintained in the fuel tank after the control valve has closed,preferably for a sufficient time to deter further refueling attemptsonce the final shutoff has occurred as described above. In theillustrative embodiment bleed vent 22p is on the order of 0.020 inchesin diameter, and temporarily maintains a refuel-preventing pressure headin the tank after refueling has ceased.

Still referring to FIG. 4, head valve 22l opens as shown in phantom topermit high volume venting of fuel vapor from the tank to the canisterthrough radial vents 22q in the ball-containing nest or cup when thedesired pressure head in the tank is exceeded.

Should the vehicle enter a rollover orientation, or if fuel slosh oroverfill levels rise to rollover head valve 22, rollover float valve 22kis forced against rollover vent outlet 22i as shown in phantom tocompletely close the valve and prevent liquid fuel from leaking to thecanister.

Referring now to FIG. 5, a first illustrative embodiment of a checkvalve 24 is illustrated for use with the system of FIG. 1. It comprisesa hollow body having an upper cylindrical plug portion 24b inserted inthe lower end of the filler pipe in a sealing, snap-retention fit. Upperplug portion 24b is provided about its circumference with seal beads 24cand a retention flange 24d for that purpose. Check valve 24 furtherincludes a hollow, cylindrical lower valve chamber 24e with a number ofradial vent ports 24f formed about its periphery. The junction of plugportion 24b and valve chamber 24e forms a valve seat 24g. The lower endof valve chamber 24e is closed by an end plate 24h with a central hole24i. A piston-like hollow valve element 24j is located in valve chamber24e for axial movement between valve seat 24g and end plate 24h. Thediameter of valve element 24j is less than the interior dimensions ofthe valve chamber, such that liquid fuel from the filler pipe flowsthrough plug portion 24b, across valve seat 24g, around valve element24j, through radial vents 24f, and into the fuel tank. Valve element 24jis normally biased against valve seat 24g by spring 24k to close thecheck valve. A resilient seal member 24l seals against valve seat 24g inthe closed position, protected from cutting or shearing by a raisedshoulder 24m on the valve element radially exterior of seal 24l. Theupper end of valve element 24j is formed as a rounded, conical flowpilot 24n which projects into plug portion 24b past seat 24g to directfuel flow around the sides of valve element 24j.

Check valve 24 is a one way, positive closing valve which opens to admitfuel from the filler pipe into the fuel tank, but which positivelycloses as soon as the refueling operation terminates and/or the pressurein the fuel tank is equal to or greater than the pressure or weight offuel in the filler pipe. In FIG. 5 check valve 24 is shown in the closedcondition, with seal 24l pressed against valve seat 24g.

Referring to FIG. 5A, when liquid fuel is introduced under pressurethrough the filler pipe into upper plug portion 24b, it forces valveelement 24j against spring 24k toward end plate 24h, opening a flow pathacross valve seat 24g and around valve element 24j through radial vents24f. The rounded, cone-shaped flow pilot 24n directs flow around theoutside of valve element 24j toward the radial vents to reduceturbulence and to generally assist flow through the check valve. As longas the force of fuel against valve element 24j is greater than the forceexerted by spring 24k and the pressure in the fuel tank, check valve 24remains in the open position of FIG. 5A.

To prevent valve element 24j from being held open by the suction effectof liquid fuel flowing through radial vents 24f at the lower end ofcheck valve 24, hole 24i formed in end plate 24h eliminates such suctioneffects by providing a make-up pressure to the lower side of valveelement 24j.

The foregoing illustrative embodiments of a system and individual valvesaccording to the present invention are exemplary in nature, and theinvention is not to be limited except as provided in the followingclaims. The invention claimed is:

We claim:
 1. A fuel level responsive control valve for controlling theventing of fuel vapor from a vehicle fuel tank to a vapor canisterduring refueling in a manner providing a shutoff cue to a person fillingthe tank, the control valve comprising:a valve adapted for venting fuelvapor from the tank to the canister at a first higher rate when the fuellevel is below an initial refueling shutoff level, at a second lowerrate when the fuel level reaches the initial refueling shutoff levelsuch that a shutoff-inducing pressure increase is temporarily created inthe tank, and for closing when a higher maximum refueling shutoff levelis reached.
 2. The control valve of claim 1, wherein the control valvecomprises a fuel level responsive float.
 3. The control valve of claim2, wherein the control valve further comprises primary and secondaryvalve elements operated by the float, such that the float seriallyplaces the primary and secondary valve elements in positions which firstpartially and then fully close the control valve.
 4. The control valveof claim 3, wherein the control valve includes a main vent outletengaged by the primary valve element at the initial refueling shutofflevel to partially close the control valve, and the primary valveelement includes a secondary vent passage in vapor communication withthe main vent outlet when the main vent outlet is engaged by the primaryvalve element, the secondary vent passage being closed by the secondaryvalve element at the maximum refueling shutoff level.
 5. The controlvalve of claim 3, wherein the control valve includes a main vent outletand a secondary vent outlet, the primary valve element being associatedwith the main vent outlet to close the main vent outlet at the initialrefueling shutoff level, and the secondary valve element beingassociated with the secondary vent outlet to close the secondary ventoutlet at the maximum refueling shutoff level.
 6. The control valve ofclaim 2 wherein the control valve comprises a single fuel levelresponsive float operatively connected to primary and secondary valveelements to serially place the primary and secondary valve elements inpartially closed and fully closed positions, respectively, as fuel levelrises to the initial and maximum refueling shutoff levels, respectively.7. The control valve of claim 6 wherein the primary and secondary valveelements are in coaxial alignment on the float.
 8. The control valve ofclaim 7, wherein the control valve includes a main vent outlet alignedwith the valve elements.
 9. The control valve of claim 6 wherein theprimary and secondary valve elements are radially offset.
 10. Thecontrol valve of claim 9, wherein the control valve includes a primaryvent outlet aligned with the primary valve element, and a secondary ventoutlet aligned with the secondary valve element.
 11. A fuel levelresponsive control valve for controlling the venting of fuel vapor froma vehicle fuel tank to a vapor canister during refueling in a mannerproviding a shutoff cue to a person filling the tank, the control valvecomprising:fuel level responsive primary and secondary valve elements inthe control valve, wherein the primary valve element is adapted to beplaced in a position partially closing fuel vapor venting through thecontrol valve by an approximate full refueling fuel level such that ashutoff-inducing pressure increase is temporarily created in the fueltank, and wherein the secondary valve element is adapted to be placed ina position fully closing fuel vapor venting through the control valve ata maximum refueling fuel level above the approximate full refuelinglevel.
 12. The control valve of claim 11 wherein the control valvecomprises a single fuel level responsive float.
 13. The control valve ofclaim 11, wherein the control valve includes a main vent outlet engagedby the primary valve element at the initial refueling shutoff level topartially close the control valve, and the primary valve elementincludes a secondary vent passage in vapor communication with the mainvent outlet when the main vent outlet is engaged by the primary valveelement, the secondary vent passage being closed by the secondary valveelement at the maximum refueling shutoff level.
 14. The control valve ofclaim 11, wherein the control valve includes a main vent outlet engagedby the primary valve element at the initial refueling shutoff level topartially close the control valve, and a secondary vent outlet engagedby the secondary valve element at the maximum refueling shutoff level tofully close the control valve.
 15. A method for controlling the ventingof fuel vapor from a vehicle fuel tank through a control valve in thetank to a vapor recovery apparatus during refueling in a mannerproviding a shutoff cue to a person filling the tank, the methodcomprising the following steps:venting fuel vapor from the tank throughthe control valve to the vapor recovery apparatus at a first higher ratewhen the fuel level is below an approximate full refueling level,partially closing the control valve when the fuel level reaches theapproximate full refueling level such that fuel vapor is vented at asecond lower rate which triggers a temporary shutoff-inducing pressureincrease in the tank, and fully closing the control valve when a highermaximum refueling fuel level is reached.
 16. The method of claim 15,further comprising the steps of venting fuel vapor through a main ventoutlet in the control valve at the first higher rate when the fuel levelis below the approximate full refueling level, partially closing themain vent outlet with a float-operated primary valve element when theapproximate full refueling level is reached, venting fuel vapor at thesecond lower rate through the partially closed main vent outlet past theprimary valve element, and fully closing the main vent outlet with afloat-operated secondary valve element when the maximum refueling fuellevel is reached.
 17. The method of claim 15, further comprising thesteps of venting fuel vapor through primary and secondary vent outletsin the control valve at the first higher rate when the fuel level isbelow the approximate full refueling level, closing the primary ventoutlet with a float-operated primary valve element when the approximatefull refueling level is reached, venting fuel vapor at the second lowerrate through the secondary vent outlet while the primary vent outlet isclosed, and closing the secondary vent outlet with a float-operatedsecondary valve element when the maximum refueling fuel level isreached.